Climate change impacts on groundwater discharge-dependent streamflow in an alpine headwater catchment.

Climate change will have-and, in much of the world, is already having-a pronounced impact on alpine water resources. A deeper understanding of the future role of groundwater in alpine catchments, including quantification of climate change impacts on groundwater discharge, is vital for understanding the future of alpine water resources as a whole. Here, we develop and couple a geophysics-informed groundwater model with a net recharge model to investigate the impacts of climate change on a nival-regime alpine headwater catchment with significant unconfined Quaternary aquifer coverage. Flow in the groundwater-fed stream at the catchment outlet is analysed to determine changes in its annual dynamics. Comparing the periods 2020-2040 and 2080-2100 under ten RCP-8.5 climate models, we find a 35 % decrease in mean groundwater discharge and an increase in no-flow periods from ~0 % to 4.3 %. We also observe significant changes to the timing of monthly mean discharge maxima and minima, which shift ~1 month and ~5 months earlier, respectively. While groundwater has the potential to dampen the impacts of snow cover loss, currently perennial nival-regime alpine streams could be at risk of becoming intermittent by the end of the century. Our study underscores the increasingly critical role that groundwater will play in alpine catchments and emphasizes the need for quantitative understanding of the limits to its buffering capacity.